Optical sub-assembly modules are used in many fields for signal conversion between optical signals and electric signals. One of the applications of optical sub-assembly module is optical transceiver which are important in optical communication. The optical transceiver serves to transfer speech or data signals from electric signals to optical signals so as to be transferred in single mode or multi-mode optical fibers to a far end. Then the optical signals are converted back to electric signals to complete a long distance transmission. One of the optical sub-assembly module frequently used is to guide light beam from a light source to an optical waveguide, such as optical fibers.
Referring to FIG. 1, a prior art coupling structure of a light source and an optical waveguide is illustrated. The prior art structure is formed by a light source 11, an optical coupling module 12, and an optical waveguide 13. The light beam from the light source 11 and then are collected by the optical coupling module 12 to be converted into a field pattern similar to that of the optical waveguide. Then the light beam is transmitted to an end face of the optical waveguide 13 to be coupled to the core of the optical waveguide 13 so that optical signals are transferred in the optical waveguide 13.
Semiconductor lasers and light emitting diodes are currently used light source 11. The optical waveguide 13 may be optical fibers or plane type integrated optic waveguide. The optical coupling module 12 may be one of a spherical lens or a aspherical lens, or a GRIN (GRadient INdex) lens, or cylindrical lens, or the combination of above components. Since above optical coupling module 12 has a bulky volume, it is not preferred for the current trend of slicing electro-optical modules. Moreover, to assemble these three optical components (light source 11, optical coupling module 12 and optical waveguide 13) will greatly increase the cost and the difficulty in package. For example, FIG. 2 shows one example of the prior art design, wherein the optical sub-assembly module includes an optical waveguide 20, a light source 21, a lens 22, a core 23, and a cladding 24. Indication 25 is a distance between the light source and the optical waveguide. In another improvement, the lens 22 is directly combined with the optical waveguide 20 so as to reduce the volume thereof.
With reference to FIG. 3, pluralities of current used structures are illustrated. Wherein in FIGS. 3b, 3c and 3d, the optical coupling modules are directly formed on the optical fibers instead of using another optical element. These designs are economical. For those illustrated in FIGS. 3a, 3e, and 3f, extra optical elements are used. No matter what methods are used, the working distance (numeral 25 in FIG. 2) is short, typically about 10 μm. Thus, it is difficult to assemble these elements. Too small working distance causes a larger reflection from the end face of the lens. As a consequence the light source is unstable.
To increasing the working distance and reduce back-reflecting light, as shown in FIG. 4-1, an optical sub-assembly module is illustrated. It contains a light source 41. The optical waveguide 43 has a core 44 and a cladding 45. The indication 46 shows the working distance between the optical waveguide 43 and light source 41. The indication 42 is a divergent angle of the light beam emitted from the light source 11. In FIG. 4-1, it is illustrated that a larger optical waveguide 43 is added before the core. The core diameter of the optical waveguide 43 has a diameter 431 larger than that of the core 44. FIG. 4-2 shows a further improvement from that shown in FIG. 4-1. In FIG. 4-2, the optical waveguide 43 is formed by high temperature thermal diffusion. The defect of this prior art is that the manufacturing time (about 1 to 2 hours) is too long to be economic. The manufacturing period is determined based on the property of fiber.
To further suppress optical back-reflection and guide light from a light source to an optical waveguide, some efforts are made in the past. Referring to FIG. 5, it is illustrated, that light beam 511 from the light source 51 is propagated through a distance 52 to an end surface 53 of the fiber. Since the end surface effect, incident light beam 511 will reflect as a reflecting light beam 512 as it incidents into the end surface 53. However, this will induce the mode hoping of the light source 51 so that the output power is unstable and thus the transmission property of the optical transceiver is affected.
To further resolve above-mentioned problem, in the prior art, some ways are used to suppress optical back-reflection and guide light from a light source to an optical waveguide. In the first method, as shown in FIG. 6, the incident light beam 611 is from a light source 61 to a optical fiber 63 having a core 631 and a cladding 632. An incident light beam 611 and a reflecting light beam 612 propagates along different paths and thus no interference to the semiconductor laser light source 61 and no interference to the transmission capability of the optical transceiver.
Referring to FIG. 7, the incident light 711 is incident into a light source 71, and an optical coupling module is added with an isolator 72 for isolating the back-reflection light 712.
Referring to FIG. 8-1(a), it illustrates a light source 811, an incident light beam 8111, a reflecting light beam 8112, a working distance 812, and an optical waveguide 813 having a core 8131 and an cladding 8132. The indication 814 is a shift and mechanic center of the optical waveguide is indicated by 815. In this prior art, the light source is inclined.
The prior arts illustrated in FIGS. 6 and 7 need high costs and complicated manufacturing process. The prior art illustrated in FIG. 8 will cause that the incident light has a greatly shift 814 from the original mechanical central shaft 815. Due to the mechanic confinement and the problem of concentricity it can be not successfully assembled to an optical transceiver module. Moreover, the shift 814 will increase the coupling time in the packaging process of the optical sub-assembly module. It should be known from those illustrated in FIGS. 8-1(b), 8-1(c) and 8-1(d), in these drawings, the components are a light source 811, an incident light beams 8114, 8115, an optical waveguide 813, searching ranges 816 and 817, optical coupling module 818 and mechanic center axis 819. In FIGS. 8-1(b) and 8-1(c), if no shift occurs, it is only necessary to search a small circle 816, while in 8-1(b) and 8-1(d), it is appreciated that under the consideration of shift, the search area is the larger circle 817 (in that the shift 814 is approximately equal to the large searching area 817). Thereby, the manufacturing time period is long.